/**
 * @param {number[]} nums
 * @return {number[]}
 */
 var getConcatenation = function(nums) {
    const ret = new Array(2*nums.length)
    for(let i = 0; i<nums.length; i++){
        ret[i] = nums[i]
    }
    const n = nums.length
    for(let i = nums.length; i<ret.length; i++){
        ret[i] = nums[i-n]
    }
    return ret
};